The present invention is in the field of tuning techniques and relates to a method for setting the parameters of a machine tool used for processing articles, such as optical inspection or metrology tool.
There is a great variety of manufacturing and technological processes whose success depend significantly on correct tuning of the parameters of a processing machine prior to its operation. The problem becomes more essential when the process contains several operational procedures requiring different values of the machine""s parameters to be set.
For example, manufacturing of semiconductor wafers is a very complicated process consisting of forming grid-like multi-layered structures, wherein several non-destructive post-process optical inspections should be carried out after different manufacturing stages. It is known that different manufacturing stages require different levels of inspection sensitivity. Inspection sensitivity prescribes, for example, a threshold according to which an inspected location is reported as fault-free or defective. Thus, for example, a post Chemical Mechanical Planarization (CMP) inspection phase typically aimed at identifying micro-scratches imposes different inspection sensitivity than that of a post etching phase aimed at pattern defects and particle identification. Incorrect inspection sensitivity, either overstated or understated, leads to undesirable results. For example, either fault-free wafers are identified as defective (due to overstated inspection sensitivity) and are, therefore, removed from the production line or really defective wafers are classified as fault free (due to understated inspection sensitivity) and therefore proceed to next production stages.
A tuning phase conventionally applied in order to reach the desired sensitivity level, typically (although not necessarily) includes the following steps. An inspection tool, which may occupy a certain working station of a production line, is set for a given inspection sensitivity level and a wafer is inspected, resulting in the provision of a list of detected locations referred to as a defect map. Then, the inspected wafer is moved from the inspection tool to a verification tool that may be accommodated within the same working station, or alternatively constitutes a stand-alone tool. The verification tool typically comprises an optical or scanning electron microscope (SEM) and utilizes high resolution imaging for verifying whether the so reported defected locations are indeed defective, or otherwise fault-free. If it is determined (after tuning, inspection and review cycle) that the number of faulty defects is too high, the wafer is returned to the inspection tool and the specified tuning, inspection-and-review cycle is repeated until the desired level of sensitivity is substantially achieved.
One example of the conventional tuning phase of the wafers inspection apparatus is disclosed in U.S. Pat. No. 5,699,447 and is schematically illustrated in FIG. 1. The apparatus, generally designated 1 includes a table 2 for receiving the wafer W to be inspected and two examining systems, generally at PH1 and PH2, for performing so-called xe2x80x9cPhase Ixe2x80x9d and xe2x80x9cPhase IIxe2x80x9d examinations, respectively, of the same wafer. To this end, as illustrated in a self-explanatory manner, table 2 is controlled by a movement control system (not shown) to effect the proper positioning of the wafer W on the table in each of the Phase I and Phase II examination phases. The system PH1 inspects the wafer W and detects suspected locations thereon having a high probability of a defect. For this purpose, a plurality of detectors 5 detect light scattered from the wafer W and transmit data representative thereof to an image processor 7, whose operation is based on a so-called xe2x80x9cDecision Tablexe2x80x9d, which makes a decision as to whether a logical output indicating the existence of a defect at a given location should be issued or not. Information indicative of these locations is stored within a storage device in a main controller 8. Only the suspected locations having a high probability of a defect are examined by the system PH2. The system PH2 carries out relatively high resolution and low speed inspection, relative to that of the system PH1 by imaging the suspected location on an opto-electric converter 9, whose output is connected to an image processor 11, which, under the control of the main controller 8, outputs information indicating the presence or absence of a defeat in each inspected location examined during Phase I. It is appreciated that Phases I and II are sequentially repeated, until the inspection sensitivity of the system PH1 reaches the correct value.
Such a conventional tuning-inspection-review phase is not only burdensome, but also time consuming, and may extend over 2-3 hours or more. If articles, which are to be inspected, progress on a production line, the production process has to be halted until the completion of the tuning phase. It should be noted that during the entire tuning-inspection-review phase the inspection and review tools may be utilized solely to this end. Put differently, during the entire period that the article undergoes review in the review tool, the inspection tool should remain in a standby mode incapable of being used in other manufacturing tasks. This disadvantage is of particular relevance when stand-alone inspection and review tools are employed. Moreover, insofar as stand-alone tools are concerned, transmitting of the article to and from the inspection and review tools results in additional loading-unloading and, consequently, known per se time consuming and error-prone handling procedures.
There is accordingly need in the art to substantially reduce or overcome the specified disadvantages by a novel method for tuning a processing machine suitable for the conditions of a specific process.
It should be noted that for convenience of explanation only the description refers by way of example only to tuning of inspection tools that inspect wafers. The invention is by no means bound to this specific example.
There is provided according to the present invention a method for setting at least one selected parameter of a processing tool that is utilized for processing articles in a production line, comprising:
a) setting said at least one selected parameter to an initial value;
b) processing an article by the processing machine and obtaining processed data indicative of features of the article, wherein said processing and obtaining the processed data are repeated a certain number of times;
c) analyzing the so obtained processed data so as to determine whether or not the processed data satisfy a predetermined result criteria;
d) upon detecting that the processed data do not satisfy the result criteria, tuning said at least one selected parameter to a tuned value; and
e) applying said steps (b), (c) and (d) as many times as required until said result criteria is essentially satisfied.
The underlying idea of the invention is to exploit the fact that inspection of articles, especially semiconductor wafers, has a statistic nature. Accordingly, several inspection procedures applied to same article, normally give rise to different inspection results. In this specific case of an optical inspection in order to locate defects, successive inspection runs provide different lists of possible defects. To this end, a certain results criteria is set, in order to determine a desired sensitivity level. Thus, for example, the result criteria may prescribe an acceptable tolerance between the inspection results obtained by a certain number of inspection procedures.
It is appreciated that the processing machine may be of any kind capable of performing inspection of articles, such as optical inspection, metrology, etc. Such a machine typically comprises illuminator and detector units and suitable light directing optics. By way of one non limiting example, the parameters which are to be set may include any one or a combination of the power of a light source used in the illuminator unit, the sensitivity of the detector unit, the autofocusing factor of the directing optics, etc. Additionally, the selected parameters may include a decision table defining the processing results. Other parameters may be used in lieu or in addition to the specified parameters, all as required and appropriate, depending upon the particular application.
It is thus evident that numerous burdensome and time-consuming steps of a conventional tuning phase are advantageously replaced here by the several steps of a certain, quickly executable model. The latter does not require the provision of any additional equipment and significantly speeds up the tuning phase.
More specifically, the present invention is used for post-process automatic optical inspection of articles progressing on a production line and is therefore described below with respect to this application.